Skip bucket durability check if CBS version < 6.6
Skip bucket durability check if CBS version < 6.6

Motivation
==========
Minimum bucket durability added for CBS version 6.6.  Integration
testing should skip check on durability level if CBS version is not >=
6.6

Modification
============
Update bucket management tests to skip min durability check if version <
6.6

Results
=======
Bucket management tests pass.

Change-Id: Iccf6169ac676b7a50a316f697f9aed6f13090a22
Reviewed-on: http://review.couchbase.org/c/couchbase-python-client/+/150033
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: David Kelly <d83cd2a93a916ce0b0d4c1349b44be044799feca@gmail.com>

couchbase/couchbase-python-client,couchbase/couchbase-python-client